1. Field of the Invention
This invention relates to a method for the production of a water-soluble conducting polyaniline or a derivative thereof. The aqueous solution of the water-soluble conducting polyaniline obtained by this method of production is made to form a thin film by such a simple technique as spin coat, dip coat, or bar coat and, therefore, can be utilized in various kinds of antistatic agents, transparent electrodes, electromagnetic wave shielding materials, photoelectric converting elements, organic electroluminescence elements, organic electrochromic elements, rustproofing agents, semiconductor photocatalysts, photoresists, nonlinear optical materials etc.
2. Description of Related Art
Since the doped polyaniline or derivative thereof features stability as a conductive polymer and enjoys inexpensiveness of the raw material to be used, the utility thereof in such applications as film electrodes, secondary cells, capacitors, antistatic agents, electromagnetic wave shielding materials etc. is now being promoted. Generally, however, the polyaniline is at a disadvantage in being insoluble and infusible and allowing no easy formation or fabrication. It is, therefore, important commercially to solubilize the polyaniline and it is most advantageous economically to render it soluble in water from the viewpoint of the equipment of production.
In recent years, therefore, various techniques for the introduction of a sulfonic acid group have been proposed with a view to imparting the water-solubility to the polyaniline. For example, such methods for polymerizing an aminobenzene sulfonic acid as a monomer as a method for synthesizing a sulfonated polyaniline by electrochemically copolymerizing aniline with an o- or a m-aminobenzene sulfonic acid (JP-A-02-166, 165), a method for copolymerizing aniline with an aminobenzene sulfonic acid by dint of chemical oxidation (JP-A-01-301,714 and JP-06-56,987), a method for sulfonating a copolymer of aniline with an aminobenzene sulfonic acid, and a derivative thereof (JP-A-05-178,989), and a method for polymerizing an o-, or a m-aminobenzene sulfonic acid by dint of electrochemical oxidation and a method for polymerizing an o- or a m-aminobenzene sulfonic acid and a derivative thereof by dint of chemical oxidation (JP-A-07-324,132 and JP-A-08-41,320) may be cited.
Further, such methods for introducing a sulfonic acid group into a polyaniline through the agency of a sulfonating agent as, for example, a method for sulfonating an emeraldine salt type polymer by using a sulfuric anhydride/phosphate triethyl complex (JP-A-61-197,633), a method for sulfonating an undoped polyaniline (emeraldine base) by using fuming sulfuric acid (WO91-06887, J. Am. Chem. Soc., 1990, vol. 112, p. 2800, J. Am. Chem. Soc., 1991, vol. 113, p. 2665), a method for sulfonating an undoped polyaniline (emeraldine base) in chlorosulfuric acid (Polymer, 1992, vol. 33, p. 4410), and a method for sulfonating the polyaniline of a leucoemeraldine base with fuming sulfuric acid (J. Am. Chem. Soc., 1996, vol. 118, p. 2545) have been proposed.
The method which copolymerizes anaminobenzene sulfonic acid and a derivative thereof with aniline by dint of electrochemical or chemical oxidation introduces only one sulfonic acid group per five aromatic rings. The product of this method, though slightly soluble in an alkali, has the problem of solubility as evinced by the fact that it is insoluble in water itself. The method which further sulfonates such a polymer introduces a little over one sulfonic group per two aromatic rings. The product of this method, though soluble in an alkali, has the problem of showing no solubility in water itself.
The method which polymerizes an o- or a m-aminobenzene sulfonic acid through electrochemical oxidation is reported to have obtained a water-soluble conducting high polymer. Since this method resorts to an electrode reaction, the product is at a disadvantage in being difficult of isolation and unfit for quantity synthesis on a commercial scale. The method for polymerizing an o- or a m-aminobenzene sulfonic acid and a derivative thereof by chemical oxidation in an acidic solution or a basic solution, on trial experiment, barely forms a reddish brown oligomer-like product and fails to produce a sulfonated polyaniline having an emeraldine salt as a repeating unit. It is, generally, difficult to obtain a polyaniline having a high molecular weight and assuming the green color peculiar to the emeraldine salt by polymerizing an aniline monomer possessing a substituent.
In the methods for introducing a sulfonic acid group by using a sulfonating agent, the method which sulfonates a polyaniline by using a sulfuric anhydride/triethyl phosphate complex attains introduction of one sulfonic acid group per five aromatic rings and has the problem of solubility as evinced by the fact that the product in the form of a conductor (doped state) is completely insoluble in water. Then, the method which attains sulfonation by using fuming sulfuric acid indeed is capable of obtaining a self-doped polyaniline having introduced one sulfonic acid group per two aromatic rings and nevertheless is at a disadvantage in exhibiting insolubility in a neutral and an acidic aqueous solution and requiring to act with an alkali to become soluble therein because the sulfonic acid group is utilized in doping the aniline. The polyaniline, however, turns into an insulator generally on acting with an alkali. For this reason, the self-doped polyaniline requires to be re-doped after solution in order to be endowed with conductivity. Thus, it does not deserve the name of a fully satisfactory entity in terms of formability and fabricability.
The method which attains sulfonation in chlorosulfuric acid indeed is capable of obtaining a self-doped polyaniline having introduced four sulfonic acid groups per five aromatic rings and nevertheless is at a disadvantage in exhibiting insolubility in a neutral and an acidic aqueous solution and requiring to act with an alkali to become soluble therein because the sulfonic acid group is utilized in doping the aniline. The product of this method, therefore, is not perfect in terms of formability and fabricability. The method which sulfonates the polyaniline of a leucoemeraldine base with fuming sulfuric acid is capable of introducing three sulfonic acid groups per four aromatic rings and still is at a disadvantage in being sparingly soluble in water because of the self-doping type of occurrence. It is not perfect in terms of solubility and formability.
Further, the methods which attain sulfonation by using such fuming sulfuric acid and chlorosulfuric acid as mentioned above invariably require to use relevant sulfonating agents in a large excess relative to polyaniline for fulfilling the sulfonation and, therefore, entail the problem that the spent acids occur in large volumes and render disposal thereof difficult.
As concrete examples of the polyaniline which is in a highly conductive state, namely in a doped state, the N-sulfonated polyaniline obtained by polymerizing diphenyl amine-4-sulfonic acid through chemical oxidation (Polymer, 1993, vol. 34, p. 158), the N-propane sulfonic acid-substituted polyaniline obtained by the reaction of polyaniline with 1,3-propane sultone (J. Am. Chem. Soc., 1994, vol. 116, p. 7939, J. Am. Chem., Soc., 1995, vol. 117, p. 10055), and the phosphonated polyaniline obtained by polymerizing o-aminobenzyl phosphonic acid through oxidation (J. Am. Chem. Soc., 1995, vol. 117, p. 8517) have been known.
The N-sulfonated polyaniline, however, has the problem of entailing unusually complicated isolation because it possesses high solubility and consequently requires high speed centrifugal separation for the purpose of effecting isolation subsequently to polymerization. Then, the N-propane sulfonic acid-substituted polyaniline is a self-doped polyaniline. This polyaniline in its doped state, therefore, is not soluble in water and is not rendered soluble in water unless it is treated by an unusually complicated procedure in terms of formability and fabricability. Further, the phosphonated polyaniline has the problem of relying for commercial manufacture on a very complicated procedure because the preparation of the o-aminobenzyl phosphonic acid as the raw material for polymerization necessitates several stages of reaction. No method which is capable of producing by a simple procedure a water-soluble polyaniline in a state possessing high conductivity, namely in a doped state, has ever been reported to the art.
Polymer films, polymer fibers, molded articles of polymer etc. are electric insulators and, therefore, are liable to assume static electricity. In consequence of this static electricity, the electronic parts using them possibly sustain breakage, adsorb dust, and even form a cause for fire. The measure to protect the electronic parts against the static electricity, therefore, has become an indispensable requirement.
Heretofore, the surfactant has been mainly used as an antistatic agent which is useful for the protection in question. The surfactant exhibits an ability to conduct ions by utilizing the moisture suspended in the air. Owing to this quality, it entails such problems as rendering it difficult to lower the surface resistance thereof below 10.sup.9.OMEGA./.quadrature. and nearly completely ceasing to manifest the antistatic effect under the condition of low humidity. Meanwhile, electron conducting type antistatic agents produced by dispersing carbon black, minute particles of such metals as aluminum, copper, and silver, and minute particles of such semiconductors as indium oxide and fluorine-doped tin oxide as fillers in general-purpose polymers have been known in the art. These fillers, however, pose such problems as using a considerably high application rate, rendering difficult the adjustment of the electric resistance because an increase in the application rate to a certain level results in a sudden fall of the electric resistance, preventing the applied layer of the antistatic agent from forming a flat smooth surface because of prominence of the fillers to the layer surface, betraying poor transparency, and imparting only insufficient strength to the applied layer of the antistatic agent.